科研之友
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摘要
Alkyladenine DNA glycosylase (AAG) is the only known human glycosylase capable of excising alkylated purines from DNA, including the highly mutagenic 1,N6-ethenoadenine (epsilonA) lesion. Here we examine AAG's ability to excise epsilonA from a nucleosome core particle (NCP), which is the primary repeating unit of DNA packaging in eukaryotes. Using chemical synthesis techniques, we assembled a global population of NCPs in which A is replaced with epsilonA. While each NCP contains no more than one epsilonA lesion, the total population contains epsilonA in 49 distinct geometric positions. Using this global epsilonA-containing NCP system, we obtained kinetic parameters of AAG throughout the NCP architecture. We observed monophasic reaction kinetics across the NCP, but varying amounts of AAG excision. AAG activity is correlated with solution accessibility and local histone architecture. Notably, we identified some highly solution-accessible lesions that are not repaired well, and an increase in repair within the region of asymmetric unwrapping of the nucleosomal DNA end. These observations support in vivo work and provide molecular-level insight into the relationship between repair and NCP architecture.
